In a wireless communication system, a RACH is used by a user terminal to establish a link with a base station for data transmission. The access via the RACH should not create undue interference on other communication links in a cell and should allow differentiation for a large group of users. The channel that the user terminal uses to establish the initial link with the base station is an RACH. The design of an RACH should meet such requirements as allowing the base station to detect access attempts easily, allow enough capacity for a large number of terminals to access the base station without undue congestion, and allow differentiation for groups of users since it is desirable for the base station to differentiate access attempts.